Emissions from cruise ships and other vessels on the Greek island of Santorini pose a significant danger to public health, a critical new report has claimed.

Air quality experts conducted tests on the island for two consecutive days this week and found pollution levels were up to 17 times higher than would be expected on a busy road.

“We found concentrations of over 340,000 particles per cubic centimetre,” said Dr. Axel Friedrich, an expert on air pollution. “In a very busy street, you will find 20,000 to 30,000.”

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An estimated two million tourists visit Santorini annually and many arrive on cruise ships, whose numbers have been capped recently due to overcrowding.

Dr. Friedrich attributes the island’s high level of air pollution to the shipping and cruise industries, which can legally use heavy fuel oil without exhaust gas cleaning systems in the Mediterranean.

“The load of air pollutants that the ships cause was enormous,” he added.

Dr. Friedrich’s research was supported by two environmental NGOs – the Hellenic Ornithological Society (HOS) in Greece and the Nature & Biodiversity Union (NABU) in Germany – which are both campaigning for a Sulphur Emission Control Area (SECA) to be established in the Mediterranean.

The North Sea and Baltic Sea both have SECAs, requiring ships entering them to burn cleaner fuel and deploy exhaust gas cleaning systems. According to NABU, air quality in some coastal areas has improved by up to 50 per cent since the limits were introduced in 2015.

The European Commission estimates that up to 50,000 people die prematurely every year in Europe due to air pollution emitted by the shipping sector. NABU claims the cost to local health services is huge and says the shipping industry must do more to reduce its emissions.

The International Maritime Organisation (IMO) claims it is working to reduce emissions. In 2016 it announced legislation that will slash sulphur emissions for vessels from 3.5 per cent to 0.5 per cent, though this isn’t due to come into effect until 2020.

“This should contribute to an improvement in air quality in and around ports,” said a spokesperson. “The feasibility of creating an IMO Emission Control Area in the Mediterranean is being looked at.”

A number of cruise lines have announced plans to introduce vessels that are more “environmentally friendly”, including Royal Caribbean and Costa Cruises, following concerns about air pollution; an earlier study by NABU claimed passengers could be inhaling 60 times more harmful pollutants than they would in natural air settings.

The British Heart Foundation issued advice for cruise passengers concerned about emissions.

“If you are worried about your health and are travelling on a cruise ship, it is best to try and minimise your exposure to air pollution by avoiding the areas near or downwind of the engine funnels – try to seek out the sea breeze on the decks,” said Philippa Hobson, a senior cardiac nurse at the charity.

“Our research shows that even short-term exposure to air pollution – just one or two hours – can have a lasting, negative impact on the heart and circulation/”

NABU claims that of all the destinations it tested at, Santorini was one of the worst for air pollution, though other Mediterranean ports had similar levels.